The present invention relate generally to braking systems for use in motor vehicles, and more particularly to an apparatus for controlling the hydraulic pressure in an accumulator used in such a braking system.
Generally, braking systems with an anti-skid control system or the like have an accumulator for accumulating hydraulic pressure to be used for the braking operation of the motor vehicle and further have an apparatus of controlling the hydraulic pressure of the accumulator. One example of such an accumulator pressure control apparatus is disclosed in Japanese Patent provisional Publication No. 58-133945, in which the hydraulic pressure in the accumulator is controlled by means of a motor-driven pump associated with a pressure sensor adapted to sense the accumulator pressure. One of problem with such an accumulator pressure control apparatus operated in connection with the pressure sensor is, however, that difficulty can be encountered to accurately keep the accumulator pressure in a predetermined range due to failures of the pressure sensor.
Furthermore, as will be understood with reference to FIG. 1, the conventional accumulator pressure control apparatus is operated such that, as shown by dotted lines Al and A2, the motor-driven pump is operated in response to the accumulator pressure being fallen down below a predetermined lower limit P2 (time T2) and deenergized when the accumulator pressure reaches a predetermined upper limit P1 by the motor-driven pump operation (time T5), FIG. 1 being a graphic illustration for showing the effect of an accumulator pressure control appratus according to the present invention (which will hereinafter be described in detail) by comparison with the prior art apparatus. Such a pump operation method causes difficulty to quickly stop the pump at the time of termination (time T4) of braking operation or slip control and causes the delay (time T5) of stop of the pump, resulting in generation of noises due to the pump operation between the times T4 and T5.